The Nervous System (Topic 8) Flashcards
What are the two major divisions of the nervous system? (1)
central and peripheral
Are neurons mitotic or amitotic? (2)
amitotic
Characteristics of neurons (2)
- Have a very high metabolic rate.
- Make up only 10% of cells in nervous system.
- The rest are glial cells. (Provide physical and metabolic support)
What is the structure of a neuron? (3)
dendrites branch from the cell body, and axon branches down from the cell body into the axon terminals
Do dendrites send or receive signals? (3)
receive
What are the different types of neurons? (3)
- bipolar (interneuron)
- unipolar (sensory neuron)
- multipolar (motoneuron)
- pyrimidal cell
What is a nucleus? (4)
cluster of cell bodies in the central nervous system (in medulla region)
What is ganglion? (4)
cluster of cell bodies in the peripheral nervous system
What is a nerve? (4)
bundle of axons that send signals to/from the CNS
What does a synapse do? (5)
releases neurotransmitters to stimulate the next cell
Cells referred to by position in relation to synapse are called what? (5)
presynaptic or postsynaptic
What are four types of glial (support) cells? (6)
- astrocytes: from tight junctions
- microglia: macrophage-like cells
- ependymal cells: ciliated (produce and circulate cerebrospinal fluid)
- oligodendrocyte: myelin
What do astrocytes do? (7)
support cells
- control extracellular environment of neurons
- Form tight junctions of the blood-brain barrier
What do microglia do? (7)
macrophage-like cells that conduct phagocytosis to remove debris
What do ependymal cells do (7)
produce and circulate CSF
What do oligodendrocytes do? (7)
they’re sheaths on multiple axons
What two types of glial cells are in the PNS? (7)
staelitle cells and shwann cells
What are satellite cells? (7)
nourish neurons
What do shwann cells do? (7)
- form myelin sheaths
- guide growth during development and regeneration
What is myelin? (8)
20-200 layers of modified plasma membrane wrapped around the axon of a neuron
What does myelin do? (8)
-insulates axon
- speeds up signals
How is myelin formed? (8)
- PNS: schwann cells
- CNS: oligodendrocytes
What is the resting membrane potential range? (10)
-40 to -90 mV
What causes change in membrane potential? (10)
ions moving in or out of the cell??
Cells, under resting conditions, are ____charged inside with respect to the extracellular fluid (10)
negatively
How is membrane potential maintained? (11)
constant breakdown of ATP
How is the concentration gradient maintained? (11)
- Na+/K+ pumps
- open ion channels “leak”
What do Na+/K+ pumps do? (11)
moves 3+ out for every 2+ that comes in, decreasing membrane potential
What do open ion channels “leak” do? (11)
- move Na+ into the cell
- move K+ out of the cell
What are two types of changes in membrane potential? (12)
graded and action potentials
What is depolarization? (12)
moving from resting membrane potential to less negative values
What is repolarization? (12)
polarization moving back to the resting membrane potential.
What is hyperpolarization? (12)
moving more negative than resting membrane potential
What are characteristics of graded potentials? (13)
- Confined to small region of the plasma membrane, so can only signal over short distances.
- Magnitude of the potential can vary.
- May be depolarizing or hyperpolarizing.
- Current is decremental:
Examples: receptor potential, synaptic potential, and pacemaker potential potential
Characteristics of action potentials (14)
- not graded, all-or-nothing
- Large change in membrane potential
- Very rapid (as brief as 1–4 ms) and may repeat at >100 Hz
What is excitability? (14)
the ability to generate action potentials
What type of cells does excitability happen in? (14)
neurons and muscle cells
Graded potential may be due to ___? (14)
Ligand-gated, mechanically-gated, and voltage-gated channels may offer the initial stimulus
What are graded potentials required for? (14)
required to trigger action potentials.
What is an action potential? (14)
Rapid depolarization and repolarization performed by voltage-gated channels
What do Na+ and K_ channels open and close in response to? (15)
- Open in response to depolarization
- Close with repolarization
Study slide 16 on action potentials!!!!
DO IT! DONT BE DUMB!
What is a threshold stimulus? (19)
a stimulus that is just strong enough to trigger an action potential
What is a subthreshold stimulus? (19)
a stimulus not strong enough to trigger an action potential
What is a subthreshold potential? (19)
a depolarization that does not reach threshold
If ‘all-or-nothing’, how do we distinguish a light touch from a pinch? (19)
the amount of action potentials (the frequency of action potentials increases)
What prevents action potentials? (20)
local anesthetics block voltage-gated sodium channels
How does blocked voltage-gated sodium channels stop pain? (20)
preventing sodium flowing, prevents depolarization, which prevents the action potential
- without the action potential, nothing is felt
How can voltage-gated sodium channel blockers lead to death? (20)
- causes no signals to be sent
- leads to cellular and respiratory failure and paralysis
What is the absolute refractory period? (21)
- a second stimulus, no matter how strong, will not produce a second action potential.
- voltage-gated Na+ channels are either open or inactivated
What is the relative refractory period? (21)
second action potential can be produced, but only if the stimulus strength is considerably greater than usual.
What does the relative refractory period correspond to? (21)
closed sodium ion channels and hyperpolarization of the membrane
What is needed to get from hyperpolarized state to threshold? (21)
bigger change in membrane potential to get from hyperpolarized state to threshold
Why does it take a smaller stimulus to reach threshold over time after hyperpolarization? (21)
over time, the membrane potential gets closer and closer to resting so it doesn’t take as much to reach threshold
(- the membrane potential is back to resting
- hyperpolarization is over
- the refractory period is over)
What does the refractory period do to the action potential? (22)
makes it unidirectional (one way)
- from the cell body to the axon terminal
Where does the first action potential take place? (22)
axon hillock/ initial segment
What has a bidirectional action potential?
muscles
What is myelin? (23)
Myelin is an insulator that makes it more difficult for charge to flow between intracellular and extracellular fluid compartments
Where do saltatory (jumps) action potentials occur? (23)
occur only at the nodes of Ranvier
- Faster than in unmyelinated neurons (100 m/s vs. 0.5 m/s).
- Membrane pumps need to restore fewer ions (metabolically cheaper).
Go through slide 24: Graded vs. Action potentials (24)
Whoop Whooop
What is a synapse? (25)
- connections between neurons/ neurons and effectors
- sites for chemical exchange
Convergence vs divergence (25)
convergence: multiple pre-synapses to single post-synapses
divergence: single pre-synapse to multiple post-synapses
How do you know you’re falling? (25)
single pre-synapse diverge to multiple post-synapses
What are two types of synapses? (26)
electrical and chemical
What are electrical synapses? (26)
electrical activity of the presynaptic neuron affects the electrical activity of the postsynaptic neuron.
- Rare, connected by gap junctions
- very fast, but no control in the second neuron
What are chemical synapses? (26)
utilize neurotransmitters.
- Pre-synaptic neurons release neurotransmitter from their axon terminals
- Neurotransmitter binds to receptors on post-synaptic neurons
- has control in the second neuron, but is slower compared to electrical
Where are neurotransmitters produced and stored? (27)
in the vesicles at the axon terminal
What is the active zone? (27)
area where vesicles are docked
How do Intracellular Ca2+ levels increase and stimulate the vesicles to bind to the plasma membrane? (27)
Via SNARE proteins
how are neurotransmitters released? (27)
exocytosis
PRACTICE SLIDE 28
YAY will be on exam
Explain slide 28
- ap reaches axon terminal
- opens calcium channels
- calcium moves in
- neurotransmitter is released
- neurotransmitter binds to ligand-gated ion channel receptor
- sodium moves in and depolarizes
- depolarization hits threshold and causes an action potential
What happens to vesicles in synaptic clefts? (29)
- Completely fuse with membrane and eventually recycled by endocytosis.
- ‘kiss-and-run fusion’
Explain the removal of a neurotransmitter (29)
- Diffusion of the transmitter from the cleft
- Degradation of the transmitter by enzymes
- Reuptake into the pre-synaptic cells for reuse
Why are neurotransmitters removed? (29)
to stop the signaling
synapses may be what? (30)
- excitatory (depolarization)
- inhibitory (hyperpolarization)
What do excitatory postsynaptic potentials (EPSP) do? (30)
bring the membrane potential closer to threshold for generating an action potential.
What do inhibitory postsynaptic potentials (EPSP) do? (30)
Make membrane potential more negative, making it harder to generate an action potential.
What are some characteristics of synaptic integration? (31)
- One EPSP is not enough to reach threshold.
- EPSPs and IPSPs may occur in the same neuron.
- Temporal summation -> from same presynaptic cell at different times.
- Spatial summation -> inputs from different locations
Can you have a graded potential that doesn’t reach threshold? (31)
yes
What does an axo-axonic synapse do? How does it regulate in the membrane? (32)
Can influence one neurons effect on another.
- Presynaptic inhibition
- Presynaptic facilitation
What do autoreceptors do? (32)
provide negative feedback on secretion of neurotransmitters
Explain what Presynaptic inhibition and facilitation is based on slide 32
A influences how much neurotransmitter comes from B
- if its more, its called facilitation
- if its less, its called inhibition
Characteristics of postsynaptic receptor regulation (32)
- can be up or down-regulated
- receptors can become desensitized (when there’s a lot of neurotransmitter, receptors desensitize)
What do many nervous system drugs act on? (33)
synaptic mechanisms
What is an agonist? (33)
increased response
What is an antagonist? (33)
inhibits response
What is botulism? What does it come from? How does it happen? (33)
- muscle paralysis
- clostridium botulinum (botulinum toxin)
- messed up canned food
What is the common name of botulinum toxin? What are its uses? (33)
- botox
- prevents wrinkles
- excessive sweating
- spasms
What does clostridium tetani (tetanus toxin) do? (33)
- Destroys SNARE proteins
- Inhibits neurotransmitter release
- Causes increased muscle contraction
What neuron does tetanus toxin target? (33)
axo-axonic inhibitor synapses
What does botulinum toxin do? (33)
interferes with SNARE proteins at excitatory synapses that activate muscles
Look through slide 34!
woo
What two classes of chemicals are presumed to be neurotransmitters? (35)
- Acetylcholine (ACh)
- Biogenic amines
What are biogenic amines? (36)
Small, charged molecules that are synthesized from amino acids.
What are catecholamines made from? (36)
tyrosine
What is acetylcholine used in? (37)
both the PNS and CNS
What are cholinergic neurons? (37)
Neurons that use ACh as the primary neurotransmitter
What are the two types of ACh receptors? (37)
- Nicotinic (Na+ ion channels)
- Muscarinic (G protein coupled) (Alter activity of a number of different enzymes and ion channels)
Where are nicotinic receptors found? (37)
at the neuromuscular junctions of skeletal muscles.
- Also found in reward pathways in the brain and autonomic ganglia
Where are muscarinic receptors found? (37)
found in brain and where PNS innervates organs & glands.
Where is ACh produced? (37)
produced in the presynaptic axon by the enzyme choline acetyl transferase (CAT)
- Acetyl CoA + choline -> acetylcholine + CoA
How is ACh degraded? (37)
acetylcholinesterase (AChE or ACE)
What do organophosphates do? (37)
inhibit ACE
How might an organophosphate kill an insect? (37)
- ACE is inhibited
- ACh increases
- too much nerve signaling and muscle contraction (overstimulated nervous system that leads to overstimulated muscle contraction)
- they will twitch till all energy is used up
Would organophosphates be hurtful to people? (37)
Yes, in large doses
What are the divisions of the PNS? (38)
- afferent (toward CNS)
- efferent (away from CNS)
Characteristics of the brain (39)
- (2% of mass, 15% of blood supply)
- Can only utilize glucose, and has virtually no reserve.
- Brain cells die in 5-10 min without blood.
What are the parts of the cerebrum? (40)
- cortex (gray matter)
- medulla (white matter)
- nuclei
What is the cortex composed of? What does it do? (40)
composed of cell bodies
- processing/ integration of signal
What is the medulla composed of? What does it do? (40)
composed of axons
- sends signals
What is the nuclei composed of? What does it do? (40)
clusters of cell bodies
- processing/integration of signals
What is the nuclei composed of? What does it do? (40)
clusters of cell bodies
- processing/integration of signals
Characteristics of the hypothalamus (41)
- Single most important controlarea for homeostasis
- Centers for processing thirst, hunger, reproduction, etc.
- Connected to the pituitary gland.
What systems does the hypothalamus bridge? (41)
endocrine and nervous systems
Characteristics of the limbic system (41)
- Spans several regions of the brain.
- Contain many nuclei.
What are the processes of the limbic system? (41)
- emotions
- motivations
- moods
- motor learning
How many pairs of cranial nerves are there? (42)
12
- motor
- sensory
- mixed
How many pairs of cranial nerves are there? (42)
12
- motor
- sensory
- mixed
What do most cranial nerves do? (42)
most innervate with the head and neck
What does the vagus nerve innervate? (42)
organs in the thorax and abdomen
What does the vagus nerve innervate? (42)
organs in the thorax and abdomen
What is the spinal cord protected by? (43)
cord protected by bone (vertebral arch)
WHat are the parts of the spinal cord? (43)
- central gray matter
- white matter
- 31 pairs of nerves (mixed)
What is the gray matter in the spinal cord made of? (43)
- Butterfly-shaped
Composed of: - Interneurons
- cell bodies
- dendrites of efferent neurons
- axons of afferent neurons
- glial cells
What is white matter in the spinal cord made of? (43)
myelinated axons
What does the somatic nervous system consist of? (44)
a single neuron between CNS and skeletal muscle cells
What does the somatic nervous system do? (44)
- innervates skeletal muscle
- can lead only to muscle excitation
is the somatic nervous system voluntary or involuntary? (44)
voluntary
What does the autonomic nervous system consist of? (44)
two-neuron chain between CNS and effector organ
What does the autonomic nervous system do? (44)
- innervates smooth and cardiac muscle, glands, and GI neurons
- can be either excitatory or inhibitory
Is the autonomic nervous system voluntary or involuntary? (44)
involuntary
What does the sympathetic nervous system do? (45)
gets you ready for stress
- “fight or flight”
What does the parasympathetic nervous system do? (45)
targets the heart (decreases heart rate)
- “rest and digest”
Make sure slide 46 makes sense to you
Yeah it makes sense
Make sure slide 47 makes sense to you
Yeahhhh it makes sense
What is an autonomic ganglion? (47)
sites at which information (action potentials) arising from the central nervous system (CNS) is transmitted to the periphery via synaptic neurotransmission
steps of parasympathetic division (47)
- action potential reaches ganglion
- ACh binds to a nicotinic receptor
- sodium channels open and lets sodium into the postsynaptic cell
- membrane potential depolarizes to threshold
- action potential is made
- calcium channels open
- SNAREs are activated?
- exocytosis occurs?
- binds to muscarinic receptors? (form G-protein)?
steps of sympathetic division (47)
go over graph on slide 47
What does the enteric nervous system do? (47)
Controls peristaltic contraction in digestive system
